Method of producing nitriding agents



2 Sheets-Sheet 1 Filed Nov. 22, 1965 Fig.2

May 2-1, 1968 A. FUCHS METHOD OF PRODUCING NITRIDING AGENTS 2Sheets-Sheet 2 Filed Nov. 22, 1965 lnvenl or:

United States Patent Office 3,384,455 Patented May 21, 1968 3,384,455METHOD OF PRODUCING NITRIDING AGENTS Alfons Fuchs, Buderich, nearDusseldorf, Germany, as-

signor to Gesellschfit fiir Elektrometallurgie m.b.H., Dusseldorf,Germany Filed Nov. 22, 1965, Ser. No. 509,090 Claims priority,application Germany, Nov. 23, 1964, G 42,078 7 Claims. (Cl. 23-191)ABSTRACT OF THE DISCLOSURE A process for producing a nitrogen-containingmetal for use as a nitriding and alloying agent which includescontacting a comminuted metal with the residual gases and the exothermicheat of reaction produced in the reaction of calcium carbide withstoichiometrically excess nitrogen to form calcium cyanamide. Suchcontact enriches the nitrogen content of the metal. Thereafter theresulting sintered nitrogen-containing metal is crushed to form abradedfines of the nitriding and alloying agent.

This invention relates to a method of producing nitriding and alloyingagents, i.e. nitrogen-containing metals or alloys, includingferro-alloys; and particularly relates to a method whereby such agentsare treated in conjunction with known processes for producing calciumcyanamide.

For nitriding and alloying steels, molten or sintered metal-containingnitriding agents are used. Molten nitrogen-containing alloy nitridingagents have the advantage of providing a high nitrogen content in thesteel, despite the fact that in relation to their content of alloyingelements they contain little nitrogen. For instance highlyrefined FeCrcontains 64 to 70% Cr but only 2 to 4% N, highly-refined FeMn contains75 to 82% Mn and only 1.5 to 2.6% N, refined FeMn contains 1% C and only1.8 to 2.2% N. However, a disadvantage possessed by employing thesealloys used in the molten state is the high cost of the nitridingprocesses, i.e. providing nitrogen in the metals or alloys.

The nitrogen-enrichment (nitriding) of alloys to produce alloy nitridingagents, 'are produced in the solid phase in special furnace plant andare rather expensive besides involving high plant-investment costs theyalso consume considerable heat, usually in the form of electricallygenerated heat, together with large volumes of nitrogen.

It is the object of the invention to provide a method for producingeffective nitriding agents which involves no significant investment costdue to the necessity of erecting special plant, and requires noadditional supply of, for instance, electrical heat, besides consumingno major volumes of specially prepared nitrogen gas. According to theinvention this is achieved by utilising, for nitriding crushedsteel-nitriding agents, the heat from the exothermic process ofproducing cyanamide from calcium carbide, and by making use of the largesurplus of nitrogen gas required in this exothermic cyanamide process.

It is well known that in the production of calcium cyanamide by theconventional methods, such as the Polzeniusz, or Frank and Caroprocesses, a considerable amount of radiant heat is generated by theexothermic reaction, and that a considerable amount of nitrogen gas isrequired, in excess of stoichiometrical quantities. This radiant heatand the excess nitrogen can be used according to the process of theinvention for nitriding the required steel-nitriding agents.

According to a preferred feature of the invention for treatingsteel-nitriding agents in conjunction with the cyanamide process, fiatsheet metal trays or containers are, by means of suitable holdingdevices, suspended in or placed on the drums into which the calciumcarbide is charged for the production of calcium cyanamide, and theagents that are to be treated are loosely charged onto the said trays orcontainers.

FIGURES 1 and 2 of the accompanying drawings illustrate a vertical andhorizontal section of such an arrangement.

The calcium cyanamide is produced in drums 1 with a refractory liningand these are conveyed on trucks, of which the top 2 of one is shown inthe drawing, through the cyanamide furnace. When the calcium carbidecharge 3 has been-charged into the drum 1, shallow pans or trays 5 areplaced onto the bracket-like supports 4 and filled with a thin layer 6of the agent which is to be nitrided.

Alternatively, the crushed agent which is to be treated may be filledinto containers of round or rectangular section. These are inserted intothe calcium carbide from which the cyanamide is to be produced. Thesides of the containers, which have an open top are perforated with anumber of holes preferably of from 2 to 8 mm. diameter, to facilitatethe entry of the nitrogen gas. Before the agent is introduced into thecontainers, the containers are lined with paper to prevent the crushedagent from falling out and from being contaminated with carbide. Theoutside of the containers may likewise be wrapped in paper to facilitatetheir subsequent extraction from the calcium cyanamide block produced inthe main process.

FIGURES 3 and 4 of the accompanying drawings are a vertical andhorizontal section respectively of such an arrangement.

So far as parts 1, 2 and 3 are concerned the arrangement is similar tothat shown in FIGURES 1 and 2. The agent which is to be treated isfilled into the open top perforated cylindrical containers 7 orrectangular containers 8, after these have been internally lined andexternally covered with paper for the above mentioned reasons.

The treatment of the metal or alloy proceeds when the carbide hasignited and the exothermic nitrogen-fixing reaction has started, in thatthe agents in the sheet metal pans or containers embedded into thecarbide is exposed to the heat of radiation generated by the reaction ofthe carbide to calcium cyanamide. The temperatures thus reached rise toa level at which the agents absorb nitrogen.

As its nitrogen content increases, the temperature of the metal or alloyalso rises and the particles sinter together. At the end of the reactiona hard slab is formed in the sheet metal trays, or hard blocks areformed in the round or rectangular section containers. During thistreatment the contents of the trays 5 and of the containers 7, 8 mustnot make direct contact with the calcium carbide from which thecyanamide forms, in order to prevent an undesirable carburisation of thenitriding agents taking place.

In numerous runs performed in a cyanamide plant on an industrial scale,nitrogen contents of 4 to 18% were obtained in the agents thus treated,for instance a highly refined ferrochrome contains 5 to 7% of nitrogen,a highly refined ferromanganese contains 4.7 to 6.6% of nitrogen, aferromanganese contains 3.5 to 4.5% of nitrogen, a chromium metalcontains 4 to 6% of nitrogen,

a ferroniobium-tantalum contains 4 to 6% of nitrogen,

and in a manganese-vanadium containing 56 to 65% V and 24 to 26% Mn, thenitrogen content was as high as 14 to 18%.

Adherence to the following conditions has been found to be very usefulfor promoting the treatment according to the invention:

(1) The nitriding agents should be ground to a particle size notexceeding 1 mm., preferably below 0.25 mm.

(2) The depth of the layer 6 of comminuted agent on the sheet metaltrays should not exceed 100 mm., and preferably it should be not morethan 60 mm.

(3) When the crushed agents are introduced in containers, round sectioncontainers may have a diameter of about 250 mm. and rectangular sectioncontainers may be between 50 and 100 mm. x 300 to 600 mm. The length ofthe containers which have an open top and a solid bottom may be /2 to /3of the depth of the carbide charge 3. With advantage the containers maybe of divided construction to permit them to be conveniently opened whenthey have been extracted from the cyanamide block, and the treatedagents to be easily removed. The side walls of these containers areperforated to facilitate the entry of the nitrogen gas. The insides ofthe containers are lined with paper and they are provided with a paperWrapping on the outside to prevent the agents from trickling out and thecarbide or cyanamide from contaminating the agents.

(4) The quantity of the agent that is to be treated should constituteonly a fraction of the carbide which is to be converted to cyanamide toensure that the radiant heat developed during the cyanamide reaction issufiicient for nitriding the agents.

(5) At the end of the process of nitrogen fixation by the carbide theagents should be carefully taken out of the trays or containers and keptseparate from the cyanamide that has been formed to preventcontamination of the nitrided sintered agents.

The method of nitriding metals or alloys to produce nitriding andalloying agents according to the invention can be performed in cyanamideplant in which either the Polzeniusz or the Frank and Caro process isperformed, the heat radiated during the exothermic calcium cyanamideprocess and the nitrogen gas excess required for its performance beingutilised. The investment cost is therefore limited to the provision ofsuitable sheet metal trays 5 and brackets 4 or of suitable containers 7or 8. The nitriding cost is very low since it makes use exclusively ofsurplus heat and surplus nitrogen gas from the cyanamide process, andconsumes only paper for lining and wrapping the containers. The labourinvolved and the wear of trays or containers is low since suitable hightemperature steels for such a purpose are readily available.

The nitrided agents which have sintered together in the form of platesin the trays or in the form of blocks in the containers are comminutedto a size that can be conveniently handled by the metallurgist. Theabraded fines are briquetted or added to fresh crushed agents andsubjected together with them to another treatment according to theinvention.

What I claim is:

1. A method of producing nitrogen-containing metal for use as anitriding and alloying agent which comprises:

(1) comminuting a metal,

(2) confining said comminuted metal in a vessel,

(3) contacting said confined comminuted metal with the residual gasesand the exothermic heat of reaction produced in a zone where calciumcarbide is reacted with nitrogen present in stoichiometric excessamounts to provide calcium cyanamide, thereby producing a sinterednitrogen-containing metal, and

(4) crushing said sintered nitrogen-containing metal.

2. The method of claim 1 wherein said metal is a metal alloy.

3. The method of claim 1 wherein said metal is confined in a perforatedvessel.

4. The method of claim 1 wherein the metal is comminuted to a grain sizebelow 1 mm.

5. The method of claim 4 wherein the metal is comminuted to a grain sizebelow 0.25 mm.

6. The method of claim 1 which includes (5) adding said crushed sinterednitrogen containing metal to additional comminuted metal and repeatingsteps (2)-(5) as long as desired.

7. The method of claim 3 wherein said perforated vessel is inserted insaid zone free from direct contact with said calcium carbide.

References Cited UNITED STATES PATENTS 10/1912 Pettibone et a1 23787/1937 Neubner 23-78 X

